1-Phenyl-1H-pyrazolo [3,4-b]pyrazine derivatives and process for preparing same

ABSTRACT

Novel 1-phenyl-1H-pyrazolo[3,4-b]pyrazine derivatives are provided which are represented by the formula: ##STR1## wherein A is (i) ##STR2## in which R 1  and R 2  are hydrogen or an alkyl, substituted alkyl, cycloalkyl, substituted cycloalkyl or amino group, or a divalent radical forming a nitrogen-containing saturated heterocyclic ring together with the nitrogen atom, (ii) ##STR3## wherein R 3  is a phenyl group which is unsubstituted or substituted by halogen or a lower alkyl, lower alokoxy, carboxyl or nitro group, and R 4  is halogen or a methyl or ethyl group, (iii)--OR 5  in which R 5  is a phenyl group which is unsubstituted or substituted by halogen or a hydroxyl, lower alkyl, lower alkoxy, amino or lower alkylamide group, or (iv)--OR 6  is an alkyl group which is unsubstituted or substituted by halogen or a phenyl, furanyl, tetrahydrofuranyl or alkylamino group. These derivatives have antitumor or antiviral activity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a 1-phenyl-1H-pyrazolo[3,4-b]pyrazine derivative having excellent antitumor or antiviral activity, which is represented by the following formula (1): ##STR4##

In the above formula (1), A stands for (i) a group ##STR5## in which R₁ and R₂ stand for a hydrogen atom, a univalent group selected from an alkyl group, a substituted alkyl group, a cycloalkyl group, a substituted cycloalkyl group and an amino group or a divalent group forming a substituted or unsubstituted, nitrogen-containing saturated heterocyclic ring together with the nitrogen atom: (ii) a group ##STR6## in which R₃ stands for a phenyl group or a substituted phenyl group in which at least one hydrogen atom is substituted by a halogen atom, a lower alkyl group, a lower alkoxy group, a carboxyl group or a nitro group, and R₄ stands for a hydrogen atom, or a methyl or ethyl group; (iii) a group --OR₅ in which R₅ stands for a phenyl group or a substituted phenyl group in which at least one hydrogen atom is substituted by a halogen atom, a hydroxyl group, a lower alkyl group, a lower alkoxy group, an amino group or a lower alkylamide group; or (iv) a group --OR₆ in which R₆ stands for an alkyl group, a cycloalkyl group or a substituted alkyl group in which at least one hydrogen atom is substituted by a halogen atom, a substituted or unsubstituted phenyl group, a furanyl group, a tetrahydrofuranyl group or an alkylamino group.

2. Description of the Prior Art

Various substances having antitumor and antiviral activities have been developed and proposed. We made researches with a view to developing a compound having an antitumor or antiviral activity and capable of being used as an antitumor or antiviral agent, and as the result, we succeeded in synthesizing noval 1-phenyl-1H-pyrazolo[3,4-b]pyrazine derivatives represented by the above formula (1) and found that these compounds have excellent antitumor and antiviral activities and are useful as an antitumor or antiviral agent.

SUMMARY OF THE INVENTION

The novel compounds of the present invention, that is, 1-phenyl-1H-pyrazol[3,4-b]pyrazine derivatives have a chemical structure represented by the following formula (1): ##STR7## wherein A stands for a group ##STR8## --OR₅ or --OR₆ and R₁ through R₆ are as defined above.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

When A in the formula (1) stands for a group ##STR9## as the alkyl group constituting the groups R₁ and R₂, there can be mentioned, for example, linear alkyl groups having 1 to 10 carbon atoms, such as methyl, ethyl, propyl, butyl, pentyl, hexyl and decanyl groups, and branched alkyl groups having 1 to 10 carbon atoms, such as 1-methylethyl, 2-methylpropyl, 1-methylpropyl, 1,1-dimethylethyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 2,2-dimethylpropyl, 1-methylbutyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,3-dimethylbutyl, 1,2-dimethylbutyl, 2,3-dimethylbutyl, 2,2-dimethylbutyl, 3,3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1-methylhexyl and 1-methylheptyl groups.

As the substituted alkyl group, there can be mentioned, for example, alkyl groups as exemplified above, in which at least one hydrogen atom is substituted by a hydroxyl group, a carboxyl group, a halogen atom, a lower alkylamino group, a phenyl group or a substituted phenyl group. As the halogen atom, there can be mentioned fluorine, chlorine and bromine, and as the alkyl group of the lower alkylamino group, there can be mentioned, for example, linear and branched alkyl groups having 1 to 6 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, isopentyl, neopentyl and hexyl groups. The substituted phenyl group is a phenyl group in which at least one hydrogen atom is substituted by an appropriate substituent. As the substituent, there can be mentioned, for example, linear and branched lower alkyl groups having 1 to 6 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, isopentyl, neopentyl and hexyl groups, halogen atoms such as fluorine, chlorine and bromine, a nitro group and a carboxyl group.

As the cycloalkyl group, there can be mentioned cycloalkyl groups having 5 to 8 carbon atoms, for example, cyclopentyl and cyclohexyl groups.

As the nitrogen-containing sautrated heterocyclic ring, there can be mentioned, for example, pyrrolidinyl, imidazolidinyl, pyrazolidinyl, piperidinyl, piperazinyl and morpholinyl groups.

These cycloalkyl and nitrogen-containing saturated heterocyclic groups may have at least one hydrogen atom thereof substituted by an appropriate substituent. As the substituent, there can be mentioned, for example, a hydroxyl group, linear and branched lower alkyl groups having 1 to 6 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, isopentyl, neopentyl and hexyl groups, halogen atoms such as fluorine, chlorine and bromine, and a nitro group and a carboxyl group.

The groups R₁ and R₂ in A are preferably a hydrogen atom or a linear or branched alkyl group having 3 to 7 carbon atoms.

When A in the formula (1) stands for a group ##STR10## as the lower alkyl group constituting a substituent of the substituted phenyl group in R₃, there can be mentioned, for example, linear and branched alkyl groups having 1 to 6 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, isopentyl and neopentyl groups. As the lower alkoxy group constituting a substituent of the substituted phenyl group in R₃, there can be mentioned, for example, linear and branched alkoxy groups having 1 to 6 carbon atoms, such as methoxy, ethoxy, propoxy, butoxy, pentyloxy and hexyloxy groups.

The group R₃ in A is preferably a phenyl group which is unsubstituted or substituted by a halogen atom or an alkyl group having 1 to 4 carbon atoms.

When A in the formula (1) stands for a group --OR₅, as the lower alkyl and lower alkoxy groups constituting substituents of the substituted phenyl group, there can be mentioned, for example, lower alkyl and lower alkoxy groups exemplified above with respect to R₃. As the lower alkylamide group, there can be mentioned, for example, linear and branched alkylamide groups having 1 to 6 carbon atoms, such as acetamide, propionamide and butylamide groups. The group R₅ is preferably a phenyl group which is unsubstituted or substituted by a halogen atom or an alkyl group having 1 to 4 carbon atoms.

When A in the formula (1) stands for a group --OR₆, as the alkyl, cycloalkyl and substituted alkyl groups, there can be mentioned, for example, alkyl, cycloalkyl and substituted alkyl groups exemplified above with respect to R₁ and R₂. The group R₆ is preferably an alkyl group having 1 to 7 carbon atoms.

The compound of the formula (1) in which A stands for a group ##STR11## can be prepared by reacting 5-substituted-1-phenyl-1H-pyrazolo[3,4-b]pyrazine of the formula (2) with the corresponding amine or nitrogen-containing heterocyclic ring compound as expressed by the following reaction formula (a): ##STR12## wherein X stands for a halogen atom, a group --SO₂ R (R is a lower slkyl group having 1 to 6 carbon atoms, a phenyl group, a methylphenyl group or an ethylphenyl group), a group --NO₂ or a group --CN, and R₁ and R₂ are as defined above.

The above-mentioned reaction (a) is carried out preferably at a temperature of 200° to 250° C. for 1 to 3 hours in a sealed tube which has been flushed with nitrogen, while an excessive amount of the amine or nitrogen-containing heterocyclic ring compound is used.

A compound of the formula (2) in which X is a chlorine atom, that is, 5-chloro-1-phenyl-1H-pyrazolo[3,4-b]pyrazine represented by the formula (2') given below, may be obtained, for example, according to the following reaction formula (b) by decarboxylation of 5-amino-1-phenylpyrazole-4-carboxylic acid of the formula (3) by heating at, for example, 180° C. to prepare 5-amino-1-phenylpyrazole of the formula (4), reaction of this compound with isoamyl nitrite in ethanol in the presence of dry hydrochloric acid to form 5-amino-4-nitroso-1-phenylpyrazole hydrochloride of the formula (5), catalytic reduction of this hydrochloride with palladium-carbon to prepare 4,5-diamino-1-phenylpyrazole of the formula (6), reaction of this compound with glyoxylic acid in water to prepare 4,5-dihydro-1-phenyl-1H-pyrazole[3,4-b]pyrazin-5-one of the formula (7) and refluxing of this compound with phosphorus oxychloride: ##STR13##

A compound of the formula (1) in which A stands for a group ##STR14## may be prepared by reacting 5-substituted-1-phenyl-1H-pyrazolo[3,4-b]pyrazine with a substituted or unsubstituted phenylamine according to the following reaction formula (a'): ##STR15## wherein X stands for a halogen atom, a group --SO₂ R (R stands for a lower alkyl group having 1 to 6 carbon atoms, a phenyl group, a methylphenyl group, or an ethylphenyl group), a group --NO₂ or a group --CN, and R₃ and R₄ are as defined above.

The above-mentioned reaction (a') is carried out preferably at a temperature of 200° to 250° C. for 1 to 3 hours in a sealed tube which has been flushed with nitrogen, while an excessive amount of the phenylamine is used.

A compound of the formula (1) in which A is a group --OR₅ may be prepared by reacting a 5-substituted-1-phenyl-1H-pyrozolo[3,4b]pyrazine of the formula (2) with the corresponding phenol derivative according to the following reaction formula (a"): ##STR16## wherein X stands for a halogen atom, a group --SO₂ --R' (R' stands for an alkyl group having 1 to 6 carbon atoms, a phenyl group, a methylphenyl group or an ethylphenyl group), a group --NO₂ or a group --CN, M is an alkali metal such as Na or K, and R₅ is as defined above.

The above-mentioned reaction (a") is carried out preferably at a temperature of 100° to 150° C. for 1 to 3 hours in dimethylsulfoxide or an alcohol while an excessive amount of the alcoholate R₅ --OM is used.

A compound of the formula (1) in which A is a group --OR₆ may be prepared by reacting a 5-substituted-1-phenyl-1H-pyrazolo[3,4-b]pyrazine of the formula (2) with the corresponding alcoholate according to the following reaction formula (a""): ##STR17## wherein X stands for a halogen atom, a group --SO₂ --R'(R' stands for an alkyl group having 1 to 6 carbon atoms, a phenyl group, a methylphenyl group or an ethylphenyl group), a group --NO₂ or a group --CN, M is an alkali metal such as Na or K and R₆ is the same as defined above.

The above-mentioned reaction (a"') may preferably be carried out under conditions similar to those which are described hereinbefore with respect to the reaction (a").

Specific examples of the compound of the present invention represented by the above-mentioned formula (1) will now be described.

    __________________________________________________________________________      ##STR18##                                                                     Com-                                  Exam-                                    pound                                 ple                                      No. R.sub.1      R.sub.2                                                                             Name of Compound                                                                               No.                                      __________________________________________________________________________     1   C.sub.3 H.sub.7                                                                             H    5-propylamino-1-phenyl-1H                                                                      1                                                              pyrazolo[3,4-b]pyrazine                                  2   C.sub.4 H.sub.9                                                                             H    5-butylamino-1-phenyl-1H                                                                       2                                                              pyrazolo[3,4-b]pyrazine                                  3   C.sub.5 H.sub.11                                                                            H    5-pentylamino-1-phenyl-1H                                                                      3                                                              pyrazolo[3,4-b]pyrazine                                                                        3                                        4   C.sub.6 H.sub.13                                                                            H    5-hexylamino-1-phenyl-1H                                                                       4                                                              pyrazolo[3,4-b]pyrazine                                  5   C.sub.10 H.sub.21                                                                           H    5-decanylamino-1-phenyl-1H                                                                     5                                                              pyrazolo[3,4-b]pyrazine                                  6   HOC.sub.2 H.sub.4                                                                           H    5-(2-hydroxyethylamino)-1-                                                                     6                                                              phenyl-1Hpyrazolo[3,4-b]-                                                      pyrazine                                                   7                                                                                 ##STR19##   H    5-(2-hydroxypropylamino)-1- phenyl-1Hpyrazolo[3,4-b]                           - pyrazine      7                                          8                                                                                 ##STR20##   H    5-(1-methylpropylamino)-1-  phenyl-1Hpyrazolo[3,4-b]                           - pyrazine      8                                          9                                                                                 ##STR21##   H    5-(2-ethylhexylamino)-1- phenyl-1Hpyrazolo[3,4-b]-                             pyrazine        9                                          10                                                                               HOOC(CH.sub.2).sub.3                                                                        H    5-(3-carboxypropylamino)-1-                                                                    10                                                             phenyl-1Hpyrazolo[3,4-b]-                                                      pyrazine                                                 11  HOOC(CH.sub.2).sub.5                                                                        H    5-(5-carboxypentylamino)-1-                                                                    11                                                             phenyl-1Hpyrazolo[3,4-b]-                                                      pyrazine                                                 12  Cl(CH.sub.2).sub.2                                                                          H    5-(2-chloroethylamino)-1-                                                                      12                                                             phenyl-1Hpyrazolo[3,4-b]-                                                      pyrazine                                                   13                                                                                ##STR22##   H    5-(2-N,Ndimethylamino- ethylamino)-1-phenyl-1H                                 pyrazolo[3,4-b]pyrazine                                                                        13                                         14                                                                                ##STR23##   H    5-benzylamino-1-phenyl-1H pyrazolo[3,4-b]pyrazine                                              14                                         15                                                                                ##STR24##   H    5-(4-nitrobenzylamino)-1- phenyl-1Hpyrazolo[3,4-b]-                            yrazine         15                                         16                                                                                ##STR25##   H    5-(4-chlorobenzylamino)-1- phenyl-1Hpyrazolo[3,4-b]-                            pyrazine       16                                         17                                                                                ##STR26##   H    5-(3-methylbenzylamino)-1- phenyl-1Hpyrazolo[3,4-b]-                            pyrazine       17                                         18                                                                               C.sub.4 H.sub.9                                                                             C.sub.4 H.sub.9                                                                     5-dibutylamino-1-phenyl-1H                                                                     18                                                             pyrazolo[3,4-b]pyrazine                                  19  HO(CH.sub.2).sub.2                                                                          CH.sub.3                                                                            5-(2-hydroxymethylamino)-1-                                                                    19                                                             phenyl-1Hpyrazolo[3,4-b]-                                                      pyrazine                                                 20                                                                                  ##STR27##   CH.sub.3                                                                            5-benzylmethylamino-1-phenyl- 1Hpyrazolo[3,4-b]pyraz                           ine             20                                         21                                                                                ##STR28##   H    5-cyclopentylamino-1-phenyl- 1Hpyrazolo 8                                      3,4-b]pyrazine  21                                         22                                                                                ##STR29##   H    5-cyclohexylamino-1-phenyl- 1Hpyrazolo[3,4-b]pyrazin                           e               22                                         23                                                                                ##STR30##   H    5-(4-methylcyclohexylamino)-1- phenyl-1Hpyrazolo[3,4                           -b]- pyrazine   23                                         24                                                                               NH.sub.2     H    5-hydrazino-1-phenyl-1H                                                                        24                                                             pyrazolo[3,4-b]pyrazine                                  25                                                                                  ##STR31##        5-piperidino-1-phenyl-1H pyrazolo[3,4-b]pyrazine                                               25                                         26                                                                                ##STR32##        5-(3-carboxypiperidion)-1-phenyl- 1Hpyrazolo[3,4-b]p                           yrazine         26                                         27                                                                                ##STR33##        5-morpholino-1-phenyl-1H pyrazolo[3,4-b]pyrazine                                               27                                       __________________________________________________________________________

    __________________________________________________________________________      ##STR34##                                                                     Compound                              Example                                  No.   R.sub.3     R.sub.4                                                                            Name of Compound                                                                               No.                                      __________________________________________________________________________     28                                                                                    ##STR35##  H   5-anilino-1-phenyl-1Hpyraz- olo[3,4-b]pyrazine                                                 28                                         29                                                                                  ##STR36##  CH.sub.3                                                                           5-Nmethylanilino-1-phenyl- 1Hpyrazolo[3,4-b]pyrazine                                           29                                         30                                                                                  ##STR37##  H   5-(2-toluidino)-1-phenyl- 1Hpyrazolo[3,4-b]pyrazine                                            30                                         31                                                                                  ##STR38##  H   5-(3-toluidino)-1-phenyl- 1Hpyrazolo[3,4-b]pyrazine                                            31                                         32                                                                                  ##STR39##  H   5-(4-toluidino)-1-phenyl-  1Hpyrazolo[3,4-b]pyrazine                                           --                                         33                                                                                  ##STR40##  H   5-(2-anisidino)-1-phenyl-  1Hpyrazolo[3,4-b]pyrazine                                           34                                         34                                                                                  ##STR41##  H   5-(3-anisidino)-1-phenyl  1Hpyrazolo[3,4-b]pyrazine                                            --                                         35                                                                                  ##STR42##  H   5-(4-anisidino)-1-phenyl-  1Hpyrazolo[3,4-b]pyrazine                                           --                                         36                                                                                  ##STR43##  H   5-(2-phenetidino)-1-phenyl- 1Hpyrazolo                                         [3,4-b]pyrazine --                                         37                                                                                  ##STR44##  H   5-(3-phenetidino)-1-phenyl- 1Hpyrazolo[3,4-b]pyrazin                           e               --                                         38                                                                                  ##STR45##  H   5-(4-phenetidino)-1-phenyl- 1Hpyrazolo[3,4-b]pyrazin                           e               35                                         39                                                                                  ##STR46##  H   5-(2-chloroanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyraz                           ine             --                                         40                                                                                  ##STR47##  H   5-(3-chloroanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyraz                           ine             --                                         41                                                                                  ##STR48##  H   5-(4-chloroanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyraz                           ine             36                                         42                                                                                  ##STR49##  H   5-(2-fluoroanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyraz                           ine             --                                         43                                                                                  ##STR50##  H   5-(3-fluoroanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyraz                           ine             --                                         44                                                                                  ##STR51##  H   5-(4-fluoroanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyraz                           ine             37                                         45                                                                                  ##STR52##  H   5-(2-bromoanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyrazi                           ne              --                                         46                                                                                  ##STR53##  H   5-(3-bromoanilino)-1-phenyl- 1Hpyrazolo[                                       3,4-b]pyrazine  --                                         47                                                                                  ##STR54##  H   5-(4-bromoanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyrazi                           ne              --                                         48                                                                                  ##STR55##  H   5-(2-nitroanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyrazi                           ne              --                                         49                                                                                  ##STR56##  H   5-(3-nitroanilino)-1-phenyl- 1Hpyrazolo[                                       3,4-b]pyrazine  38                                         50                                                                                  ##STR57##  H   5-(4-nitroanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyrazi                           ne              --                                         51                                                                                  ##STR58##  H   5-(2-ethylanilino)-1-phenyl- 1Hpytrazolo[3,4-b]pyraz                           ine             --                                         52                                                                                  ##STR59##  H   5-(3-ethylanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyrazi                           ne              --                                         53                                                                                  ##STR60##  H   5-(4-ethylanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyrazi                           ne              --                                         54                                                                                  ##STR61##  H   5-(2-propylanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyraz                           ine             --                                         55                                                                                  ##STR62##  H   5-(3-propylanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyraz                           ine             --                                         56                                                                                  ##STR63##  H   5-(4-propylanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyraz                           ine             --                                         57                                                                                  ##STR64##  H   5-(2-butylanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyrazi                           ne              '                                        58                                                                                    ##STR65##  H   5-(3-butylanilino)-1-phenyl- 1Hpyrazolo[                                       3,4-b]pyrazine  33                                         59                                                                                  ##STR66##  H   5-(4-butylanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyrazi                           ne              --                                         60                                                                                  ##STR67##  H   5-(2-carboxyanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyra                           zine            --                                         61                                                                                  ##STR68##  H   5-(3-carboxyanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyra                           zine            --                                         62                                                                                  ##STR69##  H   5-(4-carboxyanilino)-1-phenyl- 1Hpyrazolo[3,4-b]pyra                           zine            --                                         63                                                                                  ##STR70##  H   5-(2,3-dimethylanilino)-1- phenyl-1Hpyrazolo[3,4-b]-                            pyrazine       33                                         64                                                                                  ##STR71##  H   5-(2,4-dimethylanilino)-1- phenyl-1Hpyrazolo[3,4-b]-                            pyrazine       --                                         65                                                                                  ##STR72##  H   5-(2,5-dimethylanilino)-1- phenyl-1Hpyrazolo[3,4-b]-                            pyrazine       --                                         66                                                                                  ##STR73##  H   5-(2,6-dimethylanilino)-1- phenyl-1Hpyrazolo[3,4-b]-                            pyrazine       --                                         67                                                                                  ##STR74##  H   5-(3,4-dimethylanilino)-1- phenyl-1Hpyrazolo[3,4-b]-                            pyrazine       --                                         68                                                                                  ##STR75##  H   5-(3,5-dimethylanilino)-1- phenyl-1Hpyrazolo[3,4-b]-                            pyrazine       --                                       __________________________________________________________________________

    __________________________________________________________________________     (3) A = OR.sub.5                                                               Compound                                 Example                               No.   R.sub.5        Name of Compound    No.                                   __________________________________________________________________________     69                                                                                    ##STR76##     5-phenoxy-1-phenyl-1Hpyrazolo- [3,4-b]pyrazine                                                    39                                       70                                                                                  ##STR77##     5-(4-methylphenoxy)-1-phenyl-  1Hpyrazolo[3,4-b]pyraz                          ine                40                                       71                                                                                  ##STR78##     5-(4-isopropylphenoxy)-1-phenyl- 1Hpyrazolo[3,4-b]pyr                          azine              41                                       72                                                                                  ##STR79##     5-(3-aminophenoxy)-1-phenyl-  1Hpyrazolo[3,4-b]pyrazi                          ne                 42                                       73                                                                                  ##STR80##     5-(4-acetoamidophenoxy)-1-phenyl- 1Hpyrazolo[3,4-b]py                          razine             43                                       74                                                                                  ##STR81##     5-(2-methoxyphenoxy)-1-phenyl- 1Hpyrazolo[3,4-b]pyraz                          ine                44                                       75                                                                                  ##STR82##     5-(4-methoxyphenoxy)-1-phenyl- 1Hpyrazolo[3,4-b]pyraz                          ine                45                                       76                                                                                  ##STR83##     5-(4-ethoxyphenoxy)-1-phenyl- 1Hpyrazolo[3,4-b]pyrazi                          ne                 46                                       77                                                                                  ##STR84##     5-(4-hydroxyphenoxy)-1-phenyl- 1Hpyrazolo[3,4-b]pyraz                          ine                47                                       78                                                                                  ##STR85##     5-(4-chlorophenoxy)-1-phenyl- 1Hpyrazolo[3,4-b]pyrazi                          ne                 48                                       79                                                                                  ##STR86##     5-(4-bromophenoxy)-1-phenyl- 1Hpyrazolo[3,4-b]pyrazin                          e                  49                                     __________________________________________________________________________

    ______________________________________                                         (4) A = OR.sub.6                                                               Com-                                 Exam-                                     pound                                ple                                       No.   R.sub.6          Name of Compound                                                                             No.                                       ______________________________________                                         80    CH.sub.3         5-methoxy-1-phenyl-                                                                          50                                                               1Hpyrazolo-                                                                    [3,4-b]pyrazine                                         81    C.sub.2 H.sub.5  5-ethoxy-1-phenyl-                                                                           51                                                               1Hpyrazolo-                                                                    [3,4-b]pyrazine                                         82    C.sub.3 H.sub.7  5-propoxy-1-phenyl-                                                                          52                                                               1Hpyrazolo-                                                                    [3,4-b]pyrazine                                         83    isoC.sub.3 H.sub.7                                                                              5-isopropoxy-1-                                                                              53                                                               phenyl-1Hpyraz-                                                                olo[3,4-b] pyrazine                                     84    C.sub.4 H.sub.9  5-butoxy-1-phenyl-                                                                           54                                                               1Hpyrazolo-                                                                    [3,4-b]pyrazine                                         85    isoC.sub.4 H.sub.9                                                                              5-isobutoxy-1-                                                                               55                                                               phenyl-1Hpyraz-                                                                olo[3,4-b] pyrazine                                     86    secC.sub.4 H.sub.9                                                                              5-sec-butoxy-1-                                                                              56                                                               phenyl-1Hpyraz-                                                                olo[3,4-b] pyrazine                                     87    C.sub.5 H.sub.11 5-pentyloxy-1-                                                                               57                                                               phenyl-1Hpyraz-                                                                olo[3,4-b] pyrazine                                     88    isoC.sub.5 H.sub.11                                                                             5-isopentyloxy-1-                                                                            58                                                               phenyl-1Hpyraz-                                                                olo[3,4-b] pyrazine                                     89    C.sub.6 H.sub.13 5-hexyloxy-1- 59                                                               phenyl-1Hpyraz-                                                                olo[3,4-b] pyrazine                                     90    2-C.sub.6 H.sub.13                                                                              5-(2-hexyloxy)-1-                                                                            60                                              [(C.sub.4 H.sub.9)(CH.sub.3)CH]                                                                 phenyl-1Hpyraz-                                                                olo[3,4-b]pyrazine                                      91    C.sub.8 H.sub.17 5-octyloxy-1-phenyl-                                                                         61                                                               1Hpyrazolo[3,4-                                                                b]pyrazine                                              92    C.sub.6 H.sub.5CH.sub.2                                                                         5-benzyloxy-1-                                                                               62                                                               phenyl-1Hpyraz-                                                                olo[3,4-b] pyrazine                                       93                                                                                  ##STR87##       5-cyclohexyloxy-1- phenyl-1Hpyraz- olo[3,4-b]                                  pyrazine      63                                          94  C.sub.3 H.sub.7CHCHCH.sub.2                                                                     5-(trans-2-hexenyl-                                                                          64                                              (trans)          oxy)-1-phenyl-                                                                 1Hpyrazolo[3,4-                                                                b]pyrazine                                              95    (CH.sub.3).sub.2 NCH.sub.2CH.sub.2                                                              5-(2-dimethylamino-                                                                          65                                                               ethoxy)-1-phenyl-                                                              1Hpyrazolo[3,4-                                                                b]pyrazine                                                96                                                                                  ##STR88##       5-(2-tetrahydro- furfuryloxy)-1- phenyl-1Hpyraz-                               olo[3,4-b] pyrazine                                                                          66                                          97                                                                                  ##STR89##       5-(2-furfuryloxy)-1- phenyl-1Hpyraz- olo[3,4-b]                                pyrazine      67                                        ______________________________________                                    

The compounds represented by the above formula (1) have excellent antitumor and/or antiviral activities and inhibit propagation of cancerous cells and virus. Accordingly, the compounds are useful as an antitumor or antiviral agent.

The preparation of the compounds of the present invention represented by the above formula (1) will now be described in detail with reference to the following Examples.

EXAMPLES 2 THROUGH 27

These Examples illustrate the preparation of compounds of the formula (1) in which A stands for a group ##STR90##

In a sealed tube, 23.1 g (0.1 mole) of 5-chloro-1-phenyl-1H-pyrazolo[3,4-b]pyrazine was reacted with 4 moles of an amine or nitrogen-containing heterocyclic compound shown in Table 1 at 220° C. for 3 hours, and the reaction product was dissolved in chloroform. The solution was washed with dilute hydrochloric acid and then with an aqueous 10% solution of sodium carbonate and dried with sodium sulfate. The solvent was removed by distillation and the residue was recrystallized from a recrystallization solvent shown in Table 1 to obtain a compound shown in Table 1. The melting points and IR analysis values of the so-obtained compounds are shown in Table 1.

                                      TABLE 1                                      __________________________________________________________________________     Ex-                                                                            am-                                                 Melting                    ple                                Crystal Form Yield                                                                              Point                      No.                                                                               Intended Compound    Starting Amine                                                                            (Recrystallization Solvent)                                                                 (%) (°C.)                                                                        IR                                                                             ν .sub.max.sup                                                              .KBr                  __________________________________________________________________________     1  5-propylamino-1-phenyl-1H--pyrazolo                                                                 propylamine                                                                               yellow powder                                                                               78  94-95                                                                               3340                     [3,4-b]pyrazine                 (hexane)                                    2  5-butylamino-1-phenyl-1H--pyrazolo                                                                  butylamine yellow needle                                                                               75  90-92                                                                               3410                     [3,4-b]pyrazine                 (methanol)                                  3  5-pentylamino-1-phenyl-1H--pyrazolo                                                                 pentylamine                                                                               light yellow needle                                                                         63  92-93                                                                               3330                     [3,4-b]pyrazine                 (hexane)                                    4  5-hexylamino-1-phenyl-1H--pyrazolo                                                                  hexylamine yellow column                                                                               59  88-89                                                                               3350, 2860,              [3,4-b]pyrazine                 hexane                2930                  5  5-decanylamino-1-phenyl-1H--pyrazolo                                                                decanylamine                                                                              yellow needle                                                                               57       3350, 1590,              [3,4-b]pyrazine                 (methanol)            1500, 141             6  5-(2-hydroxyethylamino)-1-phenyl-1H--                                                               2-hydroxyethylamine                                                                       yellow powder                                                                               62  148-150                                                                             3300, 3350               pyrazolo[3,4-b]pyrazine         (hexane)                                    7  5-(2-hydroxypropylamino)-1-phenyl-1H-13                                                             2-hydroxypropylamine                                                                      orange powder                                                                               65  131-132                                                                             3340, 3470               pyrazolo[3,4-b]pyrazine         (methanol)                                  8  5-(1-methylpropylamino)-1-phenyl-1H--                                                               1-methylpropylamine                                                                       yellow prism 59       3310, 1590,              pryazolo[3,4-b]pyrazine         (methanol)            1510, 141             9  5-(2-ethylhexylamino)-1-phenyl-1H--                                                                 2-ethylhexylamine                                                                         yellow needle                                                                               67       3340, 1590,              pyrazolo[3,4-b]pyrazine         (methanol)            1510, 141             10 5-(3-carboxypropylamino)-1-phenyl-1H--                                                              3-carboxypropylamine                                                                      light yellow powder                                                                         76  151-153                                                                             1700                     pyrazolo[3,4-b]pyrazine         (methanol)                                  11 5-(5-carboxypentylamino)-1-phenyl-1H--                                                              5-carboxypentylamine                                                                      light yellow needle                                                                         69  151-153                                                                             1690                     pyrazolo[3,4-b]pyrazine         (methanol)                                  12 5-(2-chloroethylamino)-1-phenyl-1H--                                                                2-chloroethylamine                                                                        yellow needle                                                                               54       3360, 1590,              pyrazolo[3,4-b]pyrazine         (methanol)            1480, 141             13 5-(2-N,N--dimethylaminoethylamino)-1-                                                               2-N,N--dimethyl-                                                                          yellow needle                                                                               63  121-122                                                                             3250                     phenyl-1H--pyrazolo[3,4-b]pyrazine                                                                  aminoethylamine                                                                           (hexane)                                    14 5-bezylamino-1-phenyl-1H--pyrazolo                                                                  benzylamine                                                                               orange needle                                                                               74  130-131                                                                             3340, 3050               [3,4-b]pyrazine                 (hexane)                                    15 5-(4-nitrobenzylamine)-1-phenyl-1H--                                                                4-nitrobenzylamine                                                                        yellow powder (methanol)                                                                    68       3300, 1520,              pyrazolo[3,4-b]pyrazine                               1410                  16 5-(4-chlorobenzylamine)-1-phenyl-1H--                                                               4-chlorobenzylamine                                                                       yellow needle (methanol)                                                                    63       3310, 1600,              pyrazolo[3,4-b]pyrazine                               1410                  17 5-(3-methylbenzylamine)-1-phenyl-1H--                                                               3-methylbenzylamine                                                                       yellow powder (methanol)                                                                    71       3330, 1600,              pyrazolo[3,4-b]pyrazine                               1410                  18 5-dibutylamino-1-phenyl-1H-13 pyrazolo-                                                             dibutylamine                                                                              yellow needle (hexane)                                                                      54  38-39                                                                               3010, 2990,              [3,4-b]pyrazine                                       2920                  19 5-(2-hydroxyethylamino)-1-phenyl-                                                                   2-hydroxyethyl-                                                                           yellow plate (hexane)                                                                       65  166-167                                                                             3400                     1H-13 pyrazolo[3,4-b]pyrazine                                                                       methylamine                                            20 5-benzylmethylamino-1phenyl-1H--                                                                    benzylmethylamine                                                                         yellow plate (hexane)                                                                       59  131-132                                                                             3100                     pyrazolo[3,4-b]pyrazine                                                     21 5-cyclopentylamino-1-phenyl-1H--                                                                    cyclopentylamine                                                                          yellow needle (methanol)                                                                    78  3350, 1600,                   pyrazolo[3,4-b]pyrazine                               1490, 1410            22 5-cyclohexylamino-1-phenyl-1H--                                                                     cyclohexylamine                                                                           yellow powder (methanol)                                                                    69       3380, 1610,              pyrazolo[3,4-b]pyrazine                               1480, 1410            23 5-(4-methylcyclohexylamino)-1-phenyl-1H--                                                           4-methylcyclohexyl-                                                                       yellow scale (methanol)                                                                     71       3400, 1590,              pyrazolo[3,4-b]pyrazine                                                                             amine                            1500, 1410            24 5-hydrazine-1-phenyl-1H--pyrazolo[3,4-b]-                                                           hydrazine  yellow needle (methanol)                                                                    80  193--195                                                                            3290                     pyrazine                                                                    25 5-piperidino-1-phenyl-1H--pyrazolo-                                                                 piperidine yellow scale (methanol)                                                                     82  132-134                                                                             2930, 2850               [3,4-b]pyrazine                                                             26 5-(3-carboxypiperidino)-1-phenyl-1H--                                                               nipecotic acid                                                                            yellow needle (methanol)                                                                    68  192-194                                                                             1700                     pyrazolo[3,4-b]pyrazine                                                     27 5-morpholino-1-phenyl-1H--pyrazolo-                                                                 morpholine yellow scale (methanol)                                                                     93  163-164                                                                             2950, 2850               [3,4-b]pyrazine                                                             __________________________________________________________________________

EXAMPLES 28 THROUGH 38

In a sealed tube, 1.36 g (6 millimoles) of 5-chloro-1-phenyl-1H-pyrazolo[3,4-b]pyrazine was reacted with 25 millimoles of a phenylamine shown in Table 2 at 220° C. for 3 hours, and the reaction product was dissolved in chloroform. The solution was washed with 20 ml of 2N hydrochloric acid, then with 10 ml of an aqueous 2N solution of sodium carbonate and finally with 10 ml of water two times, and the washed solution was dried with anhydrous sodium sulfate. The solvent was removed by distillation under reduced pressure and the residue was recrystallized from a recrystallization solvent shown in Table 2 to obtain a compound shown in Table 2. The forms, yields, melting points and IR analysis values of the so-obtained compounds are shown in Table 2.

    TABLE 2       Exam-     Crystal Form    ple     (Recrystallization Yield Melting No.      R.sub.3 R.sub.4 Intended Compound Phenylamine Solvent) (%) Point      (°C.) IRν.sub.max.sup.KBr       cm.sup.-1 (NH)                                  28       ##STR91##       H 5-anilino-1-phenyl- 1Hpyrazolo[3,4-b]pyrazine       ##STR92##       yellow needle(benzene) 94 188-189 3300       29      ##STR93##       CH.sub.3 5-NMethylanilino-1-phenyl-1Hpyrazolo.sup.∥,4-b]pyrazin      e       ##STR94##       yellow needle(n-hexane) 75 97-98       30      ##STR95##       H 5-(2-toluidino)-1-phenyl-1Hpyrazolo[3,4-b]pyrazine       ##STR96##       yellow needle(methanol) 70 174-175 3280       31      ##STR97##       H 5-(3-toluidino)-1-phenyl-1Hpyrazolo[3,4-b]pyrazine       ##STR98##       yellow needle(benzene) 80 195-196 3300       32      ##STR99##       H 5-(2,3-dimethylanilino)-1-phenyl-1Hpyrazolo[3,4-b]pyrazine       ##STR100##       yellow needle(methanol) 69 163-164 3270       33      ##STR101##       H 5-(4-butylanilino)-1-phenyl-1Hpyrazolo[3,4-b]pyrazine       ##STR102##       yellow scale(benzene-n-hexane) 74 150-151 3290       34      ##STR103##       H 5-(2-anisidino)-1-phenyl-1Hpyrazolo[3,4-b]pyrazine       ##STR104##       yellow needle (methanol) 68 181-182 3320       35      ##STR105##       H 5-(4-phenetidino)-1-phenyl-1Hpyrazolo[3,4-b]pyrazine       ##STR106##       yellow scale(methanol) 70 206-207 3340       36      ##STR107##       H 5-(4-chloroanilino)-1-phenyl-1Hpyrazolo[3,4-b]pyrazine       ##STR108##       yellow powder(methanol) 72 226-227 3300       37      ##STR109##       H 5-(4-floroanilino)-1-phenyl-1Hpyrazolo[3,4-b]pyrazine       ##STR110##       yellow needle(benzene) 74 201-203 3300       38      ##STR111##       H 5-(3-nitroanilino)-1-phenyl-1Hpyrazolo[3,4-b]pyrazine       ##STR112##       yellow powder(methanol) 60 261-263 3400

EXAMPLE 39

In 5.0 (0.053 mole) of phenol was dissolved 0.34 g (0.0085 mole) of sodium hydroxide, and 1.00 g (0.0043 mole) of 5-chloro-1-phenyl-1H-pyrazolo[3,4-b]pyrazine was added to the solution. The mixture was maintained at 150° C. for 2 hours. The reaction mixture was dissolved in chloroform, and the resulting solution was washed with an aqueous 10% solution of sodium hydroxide and then dried. The solvent was removed by distillation, and the residue was recrystallized from a benzene-hexane mixed solvent to obtain 1.20 g (the yield was 92%) of 5-phenoxy-1-phenyl-1H-pyrazolo[3,4-b]pyrazine in the form of a colorless needle crystal.

EXAMPLE 40

In 3 ml of dimethyl sulfoxide were dissolved 2.00 g (0.0115 mole) of p-bromophenol and 0.5 g (0.009 mole) of potassium hydroxide, and 1.00 g (0.0043 mole) of 5-chloro-1-phenyl-1H-pyrazolo[3,4-b]pyrazine was added to the solution. The mixture was maintained at 100° C. for 2 hours. The post treatments were conducted in the same manner as described in Example 39, and the resulting residue was recrystallized from hexane to obtain 1.41 g (the yield was 89%) of 5-(4-bromophenoxy)-1-phenyl-1H-pyrazolo[3,4-b]pyrazine in the form of a colorless scaly crystal.

EXAMPLES 41 THROUGH 49

The procedures of Example 40 were repeated by using phenol derivatives shown in Table 3, and the residues were recrystallized from recrystallization solvents shown in Table 3 to obtain intended compounds shown in Table 3.

The forms, melting points and IR analysis values of the intended compounds obtained in Examples 39 through 49 are shown in Table 3.

                                      TABLE 3                                      __________________________________________________________________________                                              Form                                  Exam-                                    (Recrystal-                                                                          Melting                         ple            Phenol                    lization                                                                             Point                                                                               IRν .sub.max.sup.KB                                                         rcm.sup.-1                 No. R.sub.5    Derivative   Intented Compound                                                                           Solvent)                                                                             (°C.)                                                                        CO    Others               __________________________________________________________________________     39                                                                                  ##STR113##                                                                                ##STR114##  5-phenoxy-1-phenyl-1Hpyrazolo[3,4-b]pyrazine                                                c.n.(B + H)                                                                          116˜167                                                                       13351225                     40                                                                                ##STR115##                                                                                ##STR116##  5-(4-buromo-phenoxy-1-phenyl-1Hpyrazolo[3,4-b]                                 pyrazine     c.s.(H)                                                                              171˜172                                                                       13351250                     41                                                                                ##STR117##                                                                                ##STR118##  5-(4-methylphenoxy-1-phenyl-1Hpyrazolo[3,4-b]p                                 yrazine       c.s.(B + H)                                                                         144˜145                                                                       13351255                     42                                                                                ##STR119##                                                                                ##STR120##  5-(4-isopropylphenoxy-1-phenyl-1Hpyrazolo[3,4-                                 b]pyrazine   c.n.(H)                                                                              114˜115                                                                       13301250                     43                                                                                ##STR121##                                                                                ##STR122##  5-(3-aminophenoxy-1-phenyl-1Hpyrazolo[3,4-b]py                                 razine       c.po.(M)                                                                             173˜174                                                                       13251245                     44                                                                                ##STR123##                                                                                ##STR124##  5-(4-acetamidophenoxy-1-phenyl-1Hpyrazolo[3,4-                                 b]pyrazine   l.n.(C)                                                                              253˜254                                                                       13351250                                                                             1670(CONH)             45                                                                                ##STR125##                                                                                ##STR126##  5-(2-methylphenoxy-1-phenyl-1Hpyrazolo[3,4-b]p                                 yrazine      c.n.(M)                                                                              145˜146                                                                       13351250                     46                                                                                ##STR127##                                                                                ##STR128##  5-(4-methylphenoxy-1-phenyl-1Hpyrazolo[3,4-b]p                                 yrazine      c.s.(B)                                                                              163˜164                                                                       13351245                     47                                                                                ##STR129##                                                                                ##STR130##  5-(4-ethoxyphenoxy-1-phenyl-1Hpyrazolo[3,4-b]p                                 yrazine      c.n.(B + H)                                                                          160˜161                                                                       13351245                     48                                                                                ##STR131##                                                                                ##STR132##  5-(4-hydroxyphenoxy-1-phenyl-1Hpyrazolo[3,4-b]                                 pyrazine     c.pr.(B)                                                                             206˜207                                                                       13351245                                                                             3400(OH)               49                                                                                ##STR133##                                                                                ##STR134##  5-(4-chlorophenoxy-1-phenyl-1Hpyrazolo[3,4-b]p                                 yrazine      c.s.(H)                                                                              160˜161                                                                       13351250                   __________________________________________________________________________      Note                                                                           c . . . colorless                                                              l . . . light yellow                                                           n . . . needle                                                                 s . . . scale                                                                  pr . . . prism                                                                 po . . . powder                                                                B . . . benzene                                                                H . . . hexane                                                                 M . . . methanol                                                               C . . . chloroform                                                       

EXAMPLES 50 THROUGH 55

In 50 ml of methanol was dissolved 2.1 g (0.091 mole) of metallic sodium, and then, 9.5 g (0.043 mole) of 1-phenyl-1H-phrazolo[3,4-b]pyrazine-5-carbonitrile was added to the solution. The mixture was heated under reflux for 3 hours. After completion of the reaction, the excessive amount of methanol was removed by distillation under a reduced pressure. The residue was washed with water, dried and then recrystallized from methanol to obtain 8.2 g (the yield was 84%) of 5-methoxy-1-phenyl-1H-pyrazolo[3,4-b]pyrazine in the form of a colorless needle crystal.

The above-mentioned procedures were repeated by using various alcohols shown in Table 4 (Examples No. 51 through 55) to obtain 1-phenyl-1H-pyrazolo[3,4-b]pyrazine derivatives having in the 5-positions --OR₆ substituents shown in Table 4.

The crystal forms, yields, melting points and IR analysis values of the resultant compounds are shown in Table 4.

EXAMPLES 56, 57 AND 58

In 50 ml of sec.-butanol was dissolved 2.1 g (0.091 mole) of metallic sodium, and then, 10.0 g (0.043 mole) of 5-chloro-phenyl-1H-pyrazolo[3,4-b]pyrazine was added to the solution. The mixture was heated under reflux for 2 hours. After completion of the reaction, the excessive amount of sec.-butanol was removed by distillation under a reduced pressure. The residue was washed with water, dried and then recrystallized from hexane to obtain 6.2 g (the yield was 53%) of 5-sec.-butoxy-1-phenyl-1H-pyrazolo[3,4-b]pyrazine in the form of a colorless needle crystal.

The above-mentioned procedures were repeated by using pentyl and iso-pentyl alcohols instead of sec.-butanol to obtain 1-phenyl-1H-pyrazolo[3,4-b]pyrazine derivatives having 5-pentyloxy and 5-iso-pentyloxy groups.

The crystal forms, yields, melting points and IR analysis values of the resultant compounds are shown in Table 4.

EXAMPLES 59 THROUGH 68

In 50 ml of hexanol was dissolved 2.1 g (0.091 mole) of metallic sodium, and then, 14.6 g (0.043 mole) of 5-(4-tolylsulfonyl)-1-phenyl-1H-pyrazolo[3,4-b]pyrazine was added to the solution. The mixture was heated under reflux for 2 hours. After completion of the reaction, the exessive amount of hexanol was removed by distillation under a reduced pressure. The residue was washed with water, dried and then recrystallized from a benzene/methanol (1:2) mixed solvent to obtain 11.5 g (the yield was 90%) of 5-hexyloxy-1-phenyl-1H-pyrazolo[3,4-b]pyrazine in the form of a colorless needle crystal.

The above-mentioned procedures were repeated by using various alcohols shown in Table 4 (Examples 60 through 68) to obtain 1-phenyl-1H-pyrazolo[3,4-b]pyrazine derivatives having in the 5-positions --OR₆ substituents shown in Table 4.

The crystal forms, yields, melting points and IR analysis values of the resultant compounds are shown in Table 4.

                                      TABLE 4                                      __________________________________________________________________________                                               Crystal                                                                        form                                 Exam-                                     (Recrystal-    IRνKBr             ple                                       lization  Melting                                                                             max (cm.sup.-1)       No. R.sub.6      Alcohol       OR.sub.6   Solvent)                                                                             Yield                                                                              point                                                                               =c-o-                 __________________________________________________________________________     50  CH.sub.3     CH.sub.3 OH   5-methyl-  c.n.  84  105-107                                                                             1255                                                            (MeOH)                               51  C.sub.2 H.sub.5                                                                             C.sub.2 H.sub.5 OH                                                                           5-ethoxy-  y.n.  82  139-140                                                                             1255                                                            (MeOH)                               52  C.sub.3 H.sub.7                                                                             C.sub.3 H.sub.7 OH                                                                           5-propoxy- c.n.  89  98-99                                                                               1250                                                            (MeOH)                               53  iso C.sub.3 H.sub.7                                                                         iso C.sub.3 H.sub.7 OH                                                                       5-isoproxy-                                                                               ly.cu.                                                                               86  86-87                                                                               1255                                                            (Hexane)                             54  C.sub.4 H.sub.9                                                                             C.sub.4 H.sub.9 OH                                                                           5-butoxy-  c.sc. 90  96-98                                                                               1243                                                            (MeOH)                               55  iso C.sub.4 H.sub.9                                                                         iso C.sub.4 H.sub.9 OH                                                                       5-isobutoxy-                                                                              c.p.  88  110-111                                                                             1252                                                            (MeOH)                               56  sec C.sub.4 H.sub.9                                                                         sec C.sub.4 H.sub.9 OH                                                                       5-sec-butoxy-                                                                             c.n.  53  61-62                                                                               1255                                                            (Hexane)                             57  C.sub.5 H.sub.11                                                                            C.sub.5 H.sub.11 OH                                                                          5-pentyloxy-                                                                              c.sc. 85  98-99                                                                               1250                                                            (MeOH)                               58  iso C.sub.5 H.sub.11                                                                        iso C.sub.5 H.sub.11 OH                                                                      5-isopentyloxy-                                                                           ly.n. 83  84-85                                                                               1250                                                            (MeOH)                               59  C.sub.6 H.sub.13                                                                            C.sub.6 H.sub.13 OH                                                                          5-hexyloxy-                                                                               c.sc. 90  107-108                                                                             1250                                                            (MeOH +                                                                        Benzene)                                                                       (1:2)                                60  2-C.sub.6 H.sub.13                                                                          2-C.sub.6 H.sub.13 OH                                                                        5-(2-hexyloxy)-                                                                           c.liquid                                                                             60       1249                  61  C.sub.8 H.sub.17                                                                            C.sub.8 H.sub.17 OH                                                                          5-octyloxy-                                                                               c.sc. 81  110-111                                                                             1249                                                            (MeOH)                                 62                                                                                ##STR135##                                                                                  ##STR136##   5-benzyloxy-                                                                              c.sc.(MeOH)                                                                          90  92-93                                                                               1252                    63                                                                                ##STR137##                                                                                  ##STR138##   5-cyclohexyloxy-                                                                          c.sc.(MeOH)                                                                          71  96-97                                                                               1249                    64                                                                               C.sub.3 H.sub.7CHCHCH.sub.2                                                                 C.sub.3 H.sub.7CHCHCH.sub.2 OH                                                               5-(trans-2-                                                                               c.n.  93  55-56                                                                               1250                                                 hexenyloxy)-                                                                              (Hexane)                             65  (CH.sub.3).sub.2 NCH.sub.2CH.sub.2                                                          (CH.sub.3).sub.2 NCH.sub.2CH.sub.2 OH                                                        5-(2-dimethyl-                                                                            c.n.  94  86-87                                                                               1255                                                 aminoethyloxy)-                                                                           (Hexane)                               67                                                                                ##STR139##                                                                                  ##STR140##   5-(2-tetrahydro-furfuryloxy)                                                              c.leaflet(Hexane)                                                                    79  88-89                                                                               1243                    68                                                                                ##STR141##                                                                                  ##STR142##   5-(2-furfuryloxy)-                                                                        c.n(MeOH)                                                                            91  125-126                                                                             1251                  __________________________________________________________________________      Note                                                                           c . . . Colorless                                                              n . . . needle                                                                 ly . . . light yellow                                                          y . . . yellow                                                                 sc . . . scale                                                                 cu . . . cubic                                                                 p . . . plate                                                             

We claim:
 1. 1-phenyl-1H-pyrazolo[3,4-b]pyrazine compounds represented by the formula (1): ##STR143## wherein A stands for: (i) a group ##STR144## in which R₁ and R₂ stand for a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, said alkyl group being unsubstituted or substituted by one or two substituents selected from the group consisting of a hydroxyl group, a carboxyl group, a halogen atom, a lower alkylamino group having 1 to 6 carbon atoms, a phenyl group which is unsubstituted or substituted by one or two substituents selected from the group consisting of an alkyl group having 1 to 6 carbon atoms, a halogen atom, a nitro group and a carboxyl group;a cycloalkyl group having 5 to 8 carbon atoms, said cycloalkyl group being unsubstituted or substituted by one or two substituents selected from the group consisting of a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, a halogen atom, a nitro group and a carboxyl group; and an amino group; or R₁ and R₂ form a nitrogen-containing saturated heterocyclic ring together with the nitrogen atom, to which R₁ and R₂ are bonded, said nitrogen-containing saturated heterocyclic ring being selected from the group consisting of pyrrolidinyl, imidazolidinyl, pyrazolidinyl, piperidinyl, piperazinyl and morpholinyl groups being unsubstituted or substituted by at least one substituent selected from the group consisting of a hydroxyl group, an alkyl group having 1 to 6 carbon atoms, a halogen atom, a nitro group and a carboxyl group; (ii) a group ##STR145## in which R₃ stands for a phenyl group, said phenyl group being unsubstituted or substituted by one or two substituents selected from the group consisting of a halogen atom, a lower alkyl group having 1 to 6 carbon atoms, a lower alkoxy group having 1 to 6 carbon atoms, a carboxyl group or a nitro group, and R₄ stands for a hydrogen atom, or a methyl or ethyl group; (iii) a group --OR₅ in which R₅ stands for a phenyl group, said phenyl group being unsubstituted or substituted by one of two substituents selected from the group consisting of a halogen atom, a hydroxyl group, a lower alkyl group having 1 to 6 carbon atoms, a lower alkoxy group having 1 to 6 carbon atoms, an amino group or a lower alkylamide group having 1 to 6 carbon atoms; or (iv) a group --OR₆ in which R₆ stands for an alkyl group having 1 to 10 carbon atoms said alkyl group being unsubstituted or substituted by one or two substituents selected from the group consisting of a halogen atom, an alkylamino group having 1 to 6 carbon atoms, a furanyl group, a tetrahydrofuranyl group, a phenyl group which is unsubstituted or substituted by one or two substituents selected from the group consisting of an alkyl group having 1 to 6 carbon atoms, a halogen atom, a nitro group and a carboxyl group; or a cycloalkyl group having 5 to 8 carbon atoms.
 2. 1-phenyl-1H-pyrazolo[3,4-b]pyrazine compounds according to claim 1 wherein the groups R₁ and R₂ in A of the formula (1) are independently selected from the group consisting of a hydrogen atom and linear and branched alkyl groups having 3 to 7 carbon atoms.
 3. 1-phenyl-1H-pyrazolo[3,4-b]pyrazine compounds according to claim 1 wherein the group R₃ in A of the formula (1) is a phenyl group which is unsubstituted or substituted by a halogen atom or an alkyl group having 1 to 4 carbon atoms.
 4. 1-phenyl-1H-pyrazolo[3,4-b]pyrazine compounds according to claim 1 wherein the group R₅ in A of the formula (1) is a phenyl group which is unsubstituted or substituted by a halogen atom or an alkyl group having 1 to 4 carbon atoms.
 5. 1-phenyl-1H-pyrazolo[3,4-b]pyrazine compounds according to claim 1 wherein the group R₆ in A of the formula (1) is an alkyl group having 1 to 7 carbon atoms. 